Visual callosal connections

From: [1] Science. 5 1981;212(4496):824-7

The visual cortical areas in the two hemispheres are interconnected by axons running through the corpus callosum. In adult cats, these axons originate from, and terminate in, tangentially restricted portions of each area. In young kittens, however, callosal axons originate from the entire extent of each area, although they apparently enter the gray matter only in the restricted regions where they will also be found in adults.

Notes

Thus there is a gross overabundance of callosal fibers from the extent of whole areas and possibly across areas, but entry into gray matter is restricted to those that connect homotopic regions.

Subcortical connections

From Sur review in TINS 1990[2]

Each cortical area has a unique pattern of input and output connections. However, early in development, single cortical cells send collaterals to many targets that they later retract. Thus, motor cortex and visual cortex both project to the pyramidal tract in neonatal rats, but visual cortical cells withdraw these projections[3]

From O'Leary Ann Rev Neurosci 1994 p. 432[4]

"Indeed, at the time thalamic afferents reach their appropriate cortical area, layer 4 neurons, their principle target cells are still being generated and few if any have migrated into the cortical plate (Lund & Mustari 1977, Shatz & Luskin 1986, Reinoso & O'Leary 1990)."

Cortical Area specification

McConnell[5] [6] has evidence from heterochronic transplants that many cells are committed early to their laminar fate.

O'Leary and Stanfield [7] have reported that the development of specific cortical efferent projections can be influenced by location. They transplanted pieces of late fetal (El7) rat neocortex from visual cortex to sensorimotor cortex or vice versa, and found that the donor tissue makes final projections appropriate to the host tissue. These results suggest that some property of the surrounding host cortical tissue (such as its inputs or its location) may influence the connectivity of the donor tissue independent of its origin.



  1. Innocenti, G. M. (1981). Growth and reshaping of axons in the establishment of visual callosal connections, Science, 212(4496), 824-7 ↩︎

  2. Sur, M., Pallas, S. L., and Roe, A. W. (1990). Cross-modal plasticity in cortical development: differentiation and specification of sensory neocortex, Trends Neurosci, 13(6), 227--233 ↩︎

  3. O'Leary, D. D. (1989). Do cortical areas emerge from a protocortex?, Trends Neurosci, 12(10), 400-6 ↩︎

  4. O'Leary, D. D., Schlaggar, B. L., and Tuttle, R. (1994). Specification of neocortical areas and thalamocortical connections, Annu Rev Neurosci, 17(), 419-39 ↩︎

  5. McConnell, S. K. (1985). Migration and differentiation of cerebral cortical neurons after transplantation into the brains of ferrets, Science, 229(4719), 1268-71 ↩︎

  6. McConnell, S. K. (1988). Fates of visual cortical neurons in the ferret after isochronic and heterochronic transplantation, J Neurosci, 8(3), 945-74 ↩︎

  7. O'Leary, D. D. and Stanfield, B. B. (1989). Selective elimination of axons extended by developing cortical neurons is dependent on regional locale: experiments utilizing fetal cortical transplants, J Neurosci, 9(7), 2230-46 ↩︎